Chlorine is commonly used in water treatment processes for a variety of reasons. It is a known disinfectant, may be used to remove ammonia and other nitrogenous organic compounds, and can also provide control over objectionable taste and odor. Chlorine addition also serves to reduce color, and to control slime and algae growth.
Chlorine can be provided in gaseous form or in liquid form. Commonly utilized compounds include hydroclorites of calcium and sodium, chloramines produced via reaction of chlorine and ammonia, chloride dioxide, and chlorine donor complexes such as chlorinated cyanurates.
Recent concern has arisen over the formation of trihalomethane (THM) species in portable and industrial waters due to the alleged carcinogenicity of these materials. Conventional wisdom attributes such THM formation to chlorination.
In addition to chloroform formation, other troublesome THM species, depending on initial water chemistry and treatment parameters, may include bromodichloromethane, dibromochloromethane, bromoform, iododichloromethane, diiodochloromethane and iodoform. These species are thought to form when THM precursor compounds such as ethanol, methyl ketone, humic acid, acetone, acetaldehyde, or acetophenone, are contacted with chlorine or other halogen.
Accordingly, the desirability of attaining effective methods to reduce the formation of THMs or precursor compounds is readily apparent.